The present invention relates to a joining assembly for mounting a fastening element to an external surface of a structural member of deformable material.
Quite often it is necessary to have structural members of plastics such as plastic housings provided with fixing means enabling to mount other members to said structural members. To this end it has become known for example to press threaded inserts of a harder plastic material into respective openings of the structural members, for example by a hot melt operation, ultrasonic welding or the like. This method, however, cannot be used with thin-walled structural members such as housings of mobile telephones (cellular phones). One possibility would be to provide the structural member with an integral threaded projection by injection moulding. However this is possible only with structural members of very simple geometrical shape.
It is an object of the invention to provide an improved joining assembly for mounting a fastening element of a material of relatively higher strength to an external surface of a structural member of a material of relatively less strength.
It is a further object of the invention to provide a joining assembly for joining a fastening element and a structural member which allows to mount the fastening element to the separately manufactured structural member in a very simple manner, without the need of any bores or openings in the walls of the structural member.
In the joining assembly of the invention the fastening element comprises a main body provided with functional means and a joining flange integral with said main body, and the structural member is provided with at least one joining projection integral with the external surface thereof and engaging into a respective recess of a joining flange of the fastening element. The joining projection is provided at its free end with an upset bead provided by material deformation of the joining projection and positively retaining the joining projection to the joining flange.
This results in a positively secured surface-to-surface joint between the fastening element and the structural member which is of high resistance to twisting, withdrawal and shear stresses. Since it is not necessary to provide any bores or openings in the walls of the structural member, the walls of the structural member can be made of extremely small thickness.
The structural member is preferably made of thermoplastic material, but could be made also of light metal. In any case the structural member must be made of a material which can be deformed for making the upset bead at the end of the joining projection.
When the structural member is made of thermoplastic material, the upset bead can be made by a conventional hot melt operation such as ultrasonic welding, linear or rotation friction welding or another hot melt operation. When, however, the structural member is made of light metal, the upset bead is advantageously made by cold deformation (e.g. a riveting operation).